A pie is based on an ellipse (like an arc). The ellipse
would fit in a rectangle passed as the rect argument. The rectangle can
also be specified by its location (x, y) and its dimensions (width and height).

Inside of the parent rectangle in which an ellipse would be
drawn, you set a starting angle. This angle is measured from 0 up counted clockwise
(like the numbers of an analog clock). This means that an angle of 90 represents
6 o'clock and not 12 o'clock. This starting angle is passed as the startAngle
argument.

After specifying the starting angle, you must specify the
amount of angle covered by the pie. This also is measured clockwise. This value
is passed as the sweepAngle argument.